A group of species that utilize the same kinds of resources, such as food, nesting sites, or places to live, in a similar manner. Emphasis is on ecologically associated groups that are most likely to compete because of similarity in ecological niches, even though species can be taxonomically unrelated. The term was derived from the guild in human society composed of people engaged in an activity or trade held in common.
Richard B. Root first used the term guild in 1967, specifying the “foliage-gleaning guild” as a group of birds that habitually harvest arthropods (mainly insects and spiders) from tree leaves. In 1973 he distinguished three guilds based on feeding methods of herbivorous invertebrate animals in a community utilizing one plant species: the sap-feeding guild, the strip-feeding guild, and the pit-feeding guild. Members of the sap-feeding guild sucked juices from the plant with tubular mouthparts and included plant lice (Aphidae), frog hoppers (Cercopidae), leaf hoppers (Cicadellidae) and plant bugs (Miridae). Members of the strip-feeding guild chewed off strips of leaves with cutting mandibles or similar mechanical shears, and included caterpillars (Lepidoptera), crickets and grasshoppers (Orthoptera), and snails and slugs (Mollusca). Members of the pit-feeding guild used chewing or sucking mouthparts but concentrated feeding in small areas, resulting in many pits of consumed or damaged tissue; they included leaf beetles (Chrysomelidae), weevils (Curculionidae), and thrips (Thripidae). This was the first time that unrelated organisms were grouped into ecologically meaningful units smaller than the whole community; these groups represent the major functional roles in the community. See also: Ecological communities
The guild concept focuses attention on the ways in which ecologically related species differ enough to permit coexistence, or avoid competitive displacement. For example, new places to live for some plants are provided by badger mounds in dense tall-grass prairie vegetation. Many species were associated with these disturbances, and since mounds were relatively small and rare, the potential for competition in this guild was high. One important difference between guild members was dispersal of seeds, so that some colonized new mounds quickly and others slowly, the result being a temporal divergence in utilization. The other major difference to which plants responded was the soil moisture in mounds. The combination of these characteristics permitted many species of plants to coexist on a population of badger mounds.
Seeds provide the major source of food for many desert rodents. Studies on such granivorous rodent guilds have shown that they are highly structured in relation to body sizes of member species. In one study it was found that although species assemblages differ between the Great Basin, Mojave, and Sonoran deserts, four species per guild coexist, with distinct body sizes at about 100, 40, 20, and 7 g (3.5, 1.4, 0.7, and 0.2 oz, respectively; see illustration). This uniformity in guild composition suggests the strong influence of competition organizing the guild. See also: Population ecology
Not all guilds are as clearly structured as the granivorous rodent guild. Often the hypothesis of random assemblage of species cannot be refuted in many cases based on size differences. Much research interest is focused by ecologists on the role of competition in structuring guilds and communities.
The guild is also commonly used as the smallest unit in an ecosystem in studies relating to environmental impact, wildlife management, and habitat classification. A representative species of a guild may be selected for study involving the uncertain assumption that environmental impact will influence this species in the same way as other guild members. See also: Ecosystem